Abstract-Ultra-broadband terahertz bandpass filter with dynamically tunable attenuation based on a graphene–metal hybrid metasurface

 

Wenli Huang, Xiaoqing Luo, Yuanfu Lu, Fangrong Hu, and Guangyuan Li

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-60-22-6366

We propose an ultra-broadband terahertz bandpass filter with dynamically tunable attenuation based on a graphene–metal hybrid metasurface. The metasurface unit cell is composed of two metal stripes enclosed with a graphene rectangular ring. Results show that when the metasurface is normally illuminated by a terahertz wave polarized along the metal stripes, it can act as an ultra-broadband bandpass filter over the spectral range from 1.49 THz to 4.05 THz, corresponding to a fractional bandwidth of 92%. Remarkably, high transmittance above 90% covering the range from 1.98 THz to 3.95 THz can be achieved. By changing the Fermi level of graphene, we find that the attenuation within the passband can be dynamically tuned from 2% to 66%. We expect that the proposed ultra-broadband terahertz bandpass filter with tunable attenuation will find applications in terahertz communication and detection and sensing systems.

© 2021 Optical Society of America

Abstract-Broadband switchable terahertz half-/quarter-wave plate based on metal-VO2 metamaterials

 

Juan Luo, Xingzhe Shi, Xiaoqing Luo, Fangrong Hu, and Guangyuan Li

. Schematic of the proposed metamaterial composed of multi-layered metal-VO2${}_2$ hybrid structures. (a) When VO2${}_2$ is in the insulating state, it acts like dielectric, denoted by VO2${}_2$ (D) and indicated by the blue block, the metamaterial functions as an HWP converting linear 𝑦$y$ polarization into linear 𝑥$x$ polarization. (b) When VO2${}_2$ is in the conducting state, it acts like metal, denoted by VO2${}_2$ (M) and indicated by the red block, the metamaterial functions as a QWP converting linear 𝑦$y$ polarization into LCP. (c) Geometric parameters of the unit cell of the multi-layered metamaterial.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-21-30861&id=440195

We propose a metal-vanadium dioxide (VO2) metamaterial with broadband and functionality-switchable polarization conversion in the terahertz regime. Simulation results show that the function of the proposed metamaterial can be switched from a half-wave plate (HWP) to a quarter-wave plate (QWP) over a broad bandwidth of 0.66–1.40 THz, corresponding to a relative bandwidth of 71.8%. The HWP obtained when VO2 is in the insulating state has reflection of 90% and linear polarization conversion ratio exceeding 98% over the bandwidth of 0.58–1.40 THz. By transiting the phase of VO2 into the conducting state, the obtained QWP can convert the incident linearly-polarized wave to circularly-polarized wave with an ellipticity of 0.99 over 0.66–1.60 THz. Additionally, results show that the proposed broadband switchable HWP/QWP has a large angular tolerance. We expect that this broadband and switchable multi-functional wave plate will find applications in polarization-dependent terahertz systems including sensing, imaging, and telecommunications.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz Single-Pixel Imaging Improved by Using Silicon Wafer with SiO2 Passivation

Rongbin She, Wenquan Liu, Guanglu Wei, Yuanfu Lu, Guangyuan Li

https://www.mdpi.com/2076-3417/10/7/2427

We demonstrate terahertz single-pixel imaging is improved by using a photomodulator based on silicon passivated with SiO 2$$ . By exploring various SiO 2$$ thicknesses, we show that the modulation factor of the as-fabricated terahertz photomodulator can reach 0.9, three times that based on bare silicon. This improvement originates from chemical passivation, as well as anti-reflection. Single-pixel imaging experiments based on the compressed sensing method show that reconstructed images adopting the new photomodulator have better quality than the conventional terahertz modulator based on bare silicon. Since the passivation process is routine and low cost, we expect this work will reduce the cost of terahertz photomodulator and single-pixel THz imaging, and advance their applications.

Abstract-Single-pixel terahertz imaging based on spatial Fourier spectrum

Rongbin She, Wenquan Liu, Yuanfu Lu, Zhisheng Zhou, Guangyuan Li

http://export.arxiv.org/abs/1812.06767

We propose and demonstrate single-pixel terahertz imaging based on spatial Fourier spectrum (SFS). The concept and the operation principle of this novel approach are introduced by comparing with the conventional compressing sensing (CS) approach, clarifying their similarities and differences. By doing this, we find that these two different approaches can share the same photo-induced coded aperture setup, facilitating their direct comparisons. Our results show that, compared with the CS approach, the SFS approach can reconstruct high-quality images with greatly reduced number of measurements, i.e., the sampling ratio, and is thus more efficient. Remarkably, the SFS-based system is capable to assemble a 64x64 image with signal-to-noise ratio of 6.0 for a sampling ratio of only 4.8%. We further show that deep photo-induced terahertz modulation by adopting graphene on silicon substrate and high laser power can significantly improve the image quality. We expect this work will speed up the efficiency of single-pixel THz imaging and advance THz imaging applications.